'Divorced' Lesbians and Gays Challenging Legal Definition of a Parent : Family law: Some unconventional 'marriages' end in custody disputes. Courts are asked to validate female 'fathers.'

NEW YORK — They fell in love during the summer of 1969 and pledged their lifelong commitment in a ceremony that fall. In 1980, they had a daughter. Several years later, a son followed.

As with many relationships that end in divorce, this couple never thought it would happen to them. They were a family.

Michele G. and Nancy S., are lesbians, so they could not legally marry. Last month, six years after the couple separated, a state appeals court in San Francisco ruled that only the biological mother could claim custody of the children.

"I did the inseminating, so, literally, right from the moment of conception, I was involved," Michele said recently.

"We were like other families. We sat down to dinner together, talked, shared. And then it was gone."

Parenthood is being redefined not only by gay and lesbian couples. Through the years, parental roles have evolved to include grandparents, stepparents, foster parents, unmarried heterosexual parents and surrogate parents.

Michele's case, and a similar one under consideration in New York's highest state court, is part of a broader struggle to extend the legal definition of a parent to unconventional types of families.

"These cases are about parent-child relationships in the world we really live in, and how they aren't recognized by the courts," said Nancy Polikoff, a family law professor at American University in Washington, D.C.

"Those children considered Michele to be their mother," said Polikoff, who analyzed the debate in a recent Georgetown Law Journal article. "But we're dealing with a legal system that hasn't caught up with what's going on in American family life, and lesbian families are part of that."

When Nancy decided to leave Michele in 1985, she took the boy with her and left his sister in Michele's care. The children also spent time together several days a week at one or the other woman's home.

"For the next four years, we managed fine. At least I thought we were managing fine and Nancy didn't tell me any different. She never gave me a reason for undoing our children's lives like this," said Michele, who said she plans no further appeal.

Through her attorney, Carol Amyx, Nancy declined to be interviewed out of concern for the children's privacy. (For similar reasons, court documents in the case did not identify the women by their full names.)

Amyx said the case was not about whether Michele is a loving person or a fit caretaker.

"She is a loving person," Amyx said. "She is not a parent."

Her remark strikes to the heart of the case: What defines a parent in these days of high-tech conception?

At least 1.5 million, perhaps 4 million, children nationwide are being raised by gay or lesbian couples. Many were born of prior heterosexual unions, but about 10,000 babies have been conceived via donor insemination, according to statistics from the Lambda Legal Defense & Education Fund.

"When these couples bring a child into their relationship, it's not a haphazard thing that happens in the back of a Ford on Saturday night," said Ivy Young, head of the National Gay and Lesbian Task Force's Families Project in Washington, D.C.

"It involves joint responsibility and commitment to raising that child together," Young said. "But the technology has totally outstripped our capacity to deal with the social implications."

Experts said that Oregon and Minnesota are the only states that have broadened the right of nonbiological parents to petition for visiting rights and custody, and that no other legislation to expand parental rights for nontraditional families is pending.

As a result, courts are being pressed to define the limits on a case-by-case, state-by-state basis.

Gay couples cannot legally marry, and joint adoption has been sanctioned only in a few cases. So before a custody battle can begin, the court first must define parental rights--and who is a parent.

That definition is at the heart of a case before the Court of Appeals in Albany, N.Y., which heard arguments last month and is expected to issue a decision later this spring.

Two women, identified only as Virginia M. and Alison D., used artificial insemination to conceive and bear a son in 1981. When the relationship ended in 1983, Virginia --the mother--agreed to allow her partner regular visits with the boy.

Four years later, Virginia was dissatisfied and decided to end that arrangement. A lower court ruled in 1988 that Alison had no right to see the boy because state law generally limits visiting rights to parents, grandparents and siblings.

"Our argument is that you're either a mommy or a daddy or you're not," said attorney Anthony G. Maccarini, who represents the biological mother. "The courts protect, above all, the biological parent's rights."

Maccarini said the law may need to be expanded to accommodate unconventional domestic relationships, but he argued that the courts are not the place to establish such changes.